This invention relates to modular computing systems based on integrated circuits such as field programmable gate arrays (FPGAs) which have complex and application dependent power supply requirements.
Modular systems are well known in the electronics industry. By defining a standardized mechanical and electrical interface to a printed circuit board manufactures and industry groupings guarantee compatibility between products from various vendors. Successful module standards attract large numbers of companies who provide a wide range of compatible modules. System integrators benefit by being able to mix-and-match from these modules to create an end system tailored to customer requirements. Commonly available modules include processing (for example, cards containing microprocessors and digital signal processors or DSPs), video capture, video display, digital-to-analog (D-to-A) conversion, and network connection. By making use of these off-the-shelf devices system integrators greatly reduce their engineering costs and can bring a product to market faster. Examples of successful module formats include the TRAM format proposed by INMOS for Transputer-based systems, Texas Instrument's TIM40 format for digital signal processor (DSP) chips, Analog Devices SHARCPAC format for DSP chips and the PCI mezzanine card format.
Prior-art modular formats have been defined around the requirements of conventional microprocessors and digital signal processors. This naturally leads to bus based architectures which distribute address, data, and control signals from the processor or processors with or without additional point to point communicating sequential processes (CSP) links. Recently, field programmable gate arrays (FPGAs) have been making considerable inroads into the signal processing marketplace. FPGAs operate by implementing algorithms directly in reconfigurable logic gates: the functionality and interconnection of the logic gates is defined by a control memory which can be reprogrammed as required. With FPGAs there is no fixed bus based communications mechanism: instead programmable input/output blocks (IOBs) are configured to implement exactly those connections required by the application currently programmed onto the FPGA. Therefore, whereas a module standard for DSPs specifies the semantics of various signals on a bus a module standard based on FPGAs” needs to deliver “raw” digital connections between modules the semantics of which will be determined only once the FPGAs have been programmed. A module standard developed specifically for FPGAs by Nallatech Ltd., the assignee of the present invention is disclosed in the paper “DIME—The first module standard for FPGA Based High Performance Computing” by Malachy Devlin and Allan Cantle in Proceedings of FPL'99, Glasgow, UK September 1999, published as Springer LNCS 1673 which is incorporated by reference. The product documents “DIME Module, Physical Level 0 Specification,” part no. NT-301-0001 and “Video Processing, implementation Level 1 of the DIME Module,” NT301-0002 (both available from Nallatech Ltd., Boolean House, One Napier Park, Cumbernauld, Glasgow G68 OBH, United Kingdom) provide more detailed information on the DIME modules and are incorporated by reference.
As silicon technology scales it is becoming necessary to change the power supply voltage for integrated circuits with each process shrink. For example, 0.5-micron line width integrated circuits generally operated off 5-volt supplies, 0.35-micron integrated circuits from 3.3-volt supplies, 0.25-micron integrated circuits from 2.5-volt supplies, and the present generation of 0.18-micron circuits from 1.8-volt supplies. Since a system is normally built from many different types of integrated circuits supplied by different vendors it is very likely that there will be multiple power supplies required and multiple voltage level standards for interchip signaling. It has become increasingly common for integrated circuits to operate their input/output pins at different voltage levels from their “core” internal circuitry—this allows them to take advantage of improved process technology to increase performance while remaining compatible with older chip's signaling voltages.
Intel Corporation reacted to the need for reducing power supply voltage as process technology improves by specifying an interface between a microprocessor and a programmable power supply as shown in FIG. 1. This allowed the microprocessor to specify the power supply voltage it required. One advantage of this technology was that personal computer motherboards could be upgraded with newer processors operating off a lower power supply voltage.
An additional trend in the industry has been an explosion in the number of electrical signaling standards used to communicate between digital chips. For many years only the transistor-transistor-logic (TTL) and complementary metal oxide semiconductor (CMOS) standards were of interest—and it was easy to convert between them. Today there are many different significant standards including TTL, CMOS, low voltage differential signaling (LVDS), low voltage positive emitter coupled logic (LVPECL), and gunning transceiver logic (GTL).
FPGA manufacturers have reacted to these problems by designing complex I/O structures which are “backwardly-compatible” with previous generations of process technology and can be programmed to support many different signaling standards. This has allowed FPGAs to become the “universal connectors” at the board level which speak the signaling language of all the components in the system. The signaling standards and power supply requirements of a leading advanced FPGA family are described in “Virtex-E 1.8V Extended Memory Field Programmable Gate Array's “Preliminary Product Specification, DS025 v1.2, Sep. 19, 2000 published by Xilinx Inc. which is incorporated by reference.
As shown in FIG. 2, modern FPGAs such as Virtex-E require multiple power supply voltages. As well as the “core” power supply voltage groups or “banks” of I/O pins can operate independently at different voltage levels. Some signaling schemes also require a “reference” voltage to set the threshold at which logical ones and zeros are recognized. More details on these aspects are found in the Xilinx product specification referenced above.
Prior art module standards have not addressed the need for multiple electrical signaling standards or the requirement for modules to operate off different supply voltages. In fact, one of the basic goals of prior-art modular standards is to specify the electrical signaling standards in great detail to guarantee compatibility. This is no longer necessary given FPGAs support for multiple signaling standards.